Conventionally, in an interlayer insulating film and a surface protection film of a semiconductor element, a polyimide resin or a polybenzoxazole resin which have excellent heat resistance, electric characteristics and mechanical properties in combination has been used.
In recent years, with a further advance in integration and an increase in size of a semiconductor element, a package sealing resin has been required to be thin and small. Further, a method for surface mounting or the like by LOC (lead-on-chip) or reflow soldering has been used. Under such circumstances, there is an increasing demand for a polyimide resin which has more excellent mechanical properties, heat resistance or the like than ever.
In response to these requirements, a photosensitive polyimide obtained by imparting photosensitivity to a polyimide resin itself has come to be used. By using a photosensitive polyimide, a pattern fabricating process can be simplified, whereby a complicated production process can be shortened. A conventional photosensitive polyimide or a heat resistant photoresist using its precursor is well known, as well as its application.
As the improvement of these technologies, in recent years, a positive photosensitive resin composition which can be developed in an aqueous alkaline solution has been proposed. As for the method for producing a positive photosensitive polyimide, a method in which a 2-nitrobenzyl group is introduced into a polyimide precursor through an ester bond (Non-Patent Document 1, for example), a method in which a naphthoquinone diazide compound is mixed with soluble dihydroxylimide or a polybenzoxazole precursor (Patent Documents 1 and 2, for example), a method in which naphthoquinone diazide is mixed with a polyimide precursor (Patent Document 3, for example), and the like can be given.
A method in which an oxetane compound is added to a positive photosensitive compound is often used for preventing generation of an undeveloped part (scum) or for improving reflow resistance and solvent resistance (Patent Documents 4 and 5, for example). For these compositions, it is essential to add an aluminum complex and an active silicon compound for promoting the ring opening of the oxetane compound.
On the other hand, in recent years, in respect of a short lead time and a low cost, a surface mounting process in which an Ni film and an Au film are formed by using electroless plating, followed by attaching a solder ball by means of laser has been used more actively than ever. Electroless plating includes a step called a zincate treatment in which a treatment is conducted with a strong alkaline solution having a pH of 13 or more. Therefore, a polybenzoxazole resin or a polyimide resin having excellent resistance to this strong alkaline solution is needed (Non-Patent Document 2, for example).
However, with a conventional positive photosensitive resin composition using a polybenzoxazole resin or a polyimide resin, it is impossible to satisfy simultaneously properties such as high sensitivity and high resolution to g rays and i rays, possibility of development in a general-purpose developer and resistance to strong alkali.